Proposed legislation in California would require microchips to be implanted in cats and dogs to reduce the number of former pets killed in the state's animal shelters each year.

Under Senate Bill 236, introduced by state Sen. Jack O'Connell (D-Santa Barbara), dogs and cats would be "chipped" and the owner's identification entered in a national registry.

The bill is slated for debate in the judiciary committee next month.

Animal advocates applauded the idea but remained skeptical -- in part because of concerns that pet owners may use the microchip as a replacement for traditional identification methods.

"People think it's a Low Jack or something, and it's not," said Madeline Bernstein, president of the Los Angeles Chapter for the Society for the Prevention of Cruelty to Animals. She was referring to the tracking device that can be installed in automobiles. "A microchip should not take the place of tags. If your pet isn't tagged, people might assume it's a stray."

The Humane Society of the United States is eager to use registration statistics to track pet overpopulation, euthanasia and breeders for future legislation.

"Our position is that anything that helps animals, we support," said Bob Reder, program coordinator for the HSUS. "We don't have hard numbers and statistics on things like backyard breeders and puppy mills. It'll be good to find out who we're targeting."

According to the Society for the Prevention of Cruelty to Animals, 270,000 dogs are killed in California shelters each year. Animal rights advocates say the number of cats killed is much larger.

The American Kennel Club, which claims to maintain the largest database of microchipped pets in the country, has reunited 43,221 lost pets with owners, according to its website.

Shelters in the California county of Ventura have been implanting chips in strays for 10 years and are very familiar with the chips' performance. Only three of every 200 dogs that arrive in the county shelter on a typical day have tags, said Kathy Jenks, director of the county department of animal regulation.

"People don't want (tags) because they jingle -- or for whatever stupid reason," said Jenks. "We look at microchips like a VIN number on a car. It never goes away and no one can alter it."

Implanting the chips at a vet's office will put you back $25 to $45, Jenks said.

The shelter's $20 adoption fee includes the cost for sterilization, vaccinations and the microchip. Jenks estimates that the shelter has chipped 40,000 animals, using the InfoPetchip, which is manufactured by Trovan Technology.

The rice grain-sized device is implanted in the nape of the animal's neck using a syringe, she said. The 10-digit alphanumeric number printed on the chip is registered with InfoPet, along with a description of the animal, vaccination and sterilization records and the owner's contact information.

The chips have helped animal control authorities reunite frantic owners with pets that would have otherwise faced extermination and to keep track of nuisance animals.

In one instance, the authorities used the chip as evidence against the owner of a pit bull that had killed several neighborhood dogs and cats. Each time authorities told the owner to get rid of the dog, he lied and said he'd replaced it with a new dog. But the killings continued. Finally, animal control officers confiscated the dog and planted a chip in it. The next time the pit bull terrorized the neighborhood, the officers could prove the man had never replaced it.

But the technology isn't perfect, said Jenks, who tested four different microchips on the office dog before choosing one for use at the shelter.

Chips made by one manufacturer can't be read by another manufacturer's scanner. Also, the chips migrate; one of the chips used on the office dog ended up in its leg. Some scanners read a chip from a distance of 14 inches while others can't detect a chip that is more than an inch away -- a limitation that can prove dangerous with rabid dogs, Jenks said.

"I appreciate what O'Connell is trying to do, but the technology just isn't there yet," Jenks said. "It needs to be standardized."

Privacy was a concern for one pet owner.

"I just don't like the idea of another government database having my personal information in it," said Kate Jimenez, a Lompoc housewife who owns two dogs and three cats. "It's just one more way of registering people. Twenty years from now, they'll want to chip infants before they leave the hospital."